Power control systems are used to control the rate of delivery of power to a member which requires power or which performs work. For example, power control systems are used to control the delivery of electrical power to a load (eg. a motor or other electromechanical devices which produce work such as solenoids, loudspeakers, florescent lights, incandescent lights and sodium lamps). The load may also be a battery wherein the power control system is used to control the charging and/or the discharging of the battery. Power control systems are also used in mechanical systems such as to control the delivery of power from an internal combustion engine. Examples of power control systems for such mechanical systems include governors and regulators for power generators.
Historically, power control systems have been designed to provide a uniform flow of power. For example, in the case of electrical motors, power delivery systems have been developed so as to ensure a continuous flow of electricity to a motor so that the drive shaft driven by the motor runs at a constant rate of revolution. In this way, the motor operates smoothly (i.e. without any vibrations). Similarly, even in mechanical systems, such as the use of an internal combustion engine to drive a vehicle (e.g. a car, train, airplane or the like), the power control systems have been developed so as to ensure that the engine provides smooth acceleration to the vehicle.
More recently, developments have been directed also towards decreasing the power requirements of a system. Typically, such work has been developed to reduce the actual amount of power required to operate the system while still maintaining a uniform flow of power. Examples of such developments include improved laminations and wiring for motors and generators to reduce power lost as heat.
There are also many applications wherein no power control system is utilized. An example of this is lighting. Fundamentally, an incandescent light bulb has a filament, usually contained within a glass enclosure, filled with a gas selected to maximize filament life. In use, an electric current is passed through the filament and simply serves to heat the filament to a very high temperature. The effect of this is to cause the filament to radiate electromagnetic radiation. It is well known that the spectrum of radiation produced is dependent upon the temperature of the filament. The filament is designed to reach temperatures such that a significant proportion of the radiation falls within the visible band of the electromagnetic spectrum. Unfortunately, the electromagnetic spectrum produced by a heated object, such as a filament, is necessarily broad, and much of the radiation falls either in the infrared or ultraviolet bands. This is highly undesirable. However, conventionally, it has simply been accepted that the physics of radiation or a heated body necessarily determines characteristic. Accordingly, this is simply accepted, and common incandescent light bulbs have a relatively low efficiency.
Similarly, a fluorescent light bulb typically has a gas, eg. mercury vapour, contained within a glass enclosure. In use, an electric current is passed through the mercury vapour to ionize the vapour, This in turn excites a fluorescent coating on the glass, to produce visible light as well as electromagnetic radiation outside the visible spectrum.
Another example are electric motors and other devices which are powered by batteries or cells. Batteries or cells are commonly classified into two types, namely: primary cells, which are single use cells and, after discharge, cannot be recharged for further use; and secondary cells or batteries, which are subjected to a large number of charge and discharge cycles. Commonly, the current or energy drain from a battery or cell, whether this be a primary cell or secondary cell, is determined solely by the characteristics of the load. While there are a number of concepts employing pulse width modulation which are used to control the power consumption of electric motors, these known techniques are directed solely to controlling the motor, without regard to the effect on the energy source, and in particular without regard to any impact on the drain from a battery source.
Secondary batteries or cells deliver a DC current. Accordingly, charging of such secondary cells is commonly done by connection to a suitable, fixed DC potential. Current flow into the cell is then determined by the electrical characteristics of the cell, including the internal resistance of the cell. Practically, when charging the cell, the current initially has a relatively high value, and then reduces down, in some approximate exponential fashion. When a secondary battery is recharged, heat is produced. This heat is a byproduct of the recharging process and constitutes a loss of energy when a battery or cell is recharged. The speed at which a secondary battery or cell can be recharged is generally governed by the temperature to which the battery may be raised without degradation of the battery occurring.
Despite the advances which have been made in recent years in power control systems, a need still exists to increase the energy efficiency of electrical and mechanical devices as well as the speed and efficiency of battery recharging.